Acceleration of the Antarctic Circumpolar Current by Wind Stress along the Coast of Antarctica

The influence of wind forcing on variability of the Antarctic Circumpolar Current (ACC) is investigated using a series of eddy-permitting ocean–sea ice models. At interannual and decadal time scales the ACC transport is sensitive to both the mean strength of westerly winds along the ACC circumpolar path, consistent with zonal momentum balance theories, and sensitive to the wind stresses along the coast of Antarctica, consistent with the “free mode” theory of Hughes et al. A linear combination of the two factors explains differences in ACC transport across 11 regional quasi-equilibrium experiments. Repeated single-year global experiments show that the ACC can be robustly accelerated by both processes. Across an ensemble of simulations with realistic forcing over the second half of the twentieth century, interannual ACC transport variability owing to the free-mode mechanism exceeds that due to the zonal momentum balance mechanism by a factor of between 3.5 and 5 to one. While the ACC transport may not accelerate significantly owing to projected increases in along-ACC winds in future decades, significant changes in transport could still occur because of changes in the stress along the coast of Antarctica.